Abstract
Despite the remarkable complexity of the individual neuron and of neuronal circuits, it has been clear for quite a while that, in order to understand the functioning of the brain, the contribution of other cell types in the brain have to be accounted for. Among glial cells, astrocytes have multiple roles in orchestrating neuronal functions. Their communication with neurons by exchanging signaling molecules and removing molecules from extracellular space takes place at several levels and is governed by different cellular processes, supported by multiple cellular structures, including the cytoskeleton. Intermediate filaments in astrocytes are emerging as important integrators of cellular processes. Astrocytes express five types of intermediate filaments: glial fibrillary acidic protein (GFAP); vimentin; nestin; synemin; lamins. Variability, interactions with different cellular structures and the particular roles of individual intermediate filaments in astrocytes have been studied extensively in the case of GFAP and vimentin, but far less attention has been given to nestin, synemin and lamins. Similarly, the interplay between different types of cytoskeleton and the interaction between the cytoskeleton and membranous structures, which is mediated by cytolinker proteins, are understudied in astrocytes. The present review summarizes the basic properties of astrocytic intermediate filaments and of other cytoskeletal macromolecules, such as cytolinker proteins, and describes the current knowledge of their roles in normal physiological and pathological conditions.
Highlights
The first observation of neuroglia, made by Rudolf Virchow in 1858, was rather dubious.He described it as a substance with a somewhat static role of holding together and giving form to the nervous parts
glial fibrillary acidic protein (GFAP) is upregulated in both the A1 and A2 reactive astrocytes, whereas vimentin expression is more prominent, and nestin and plectin appear to be exclusively upregulated in the A2 subtype
Mice, resulting in an increase in immune cell infiltration [106]. This line of evidence suggests that the intermediate filaments (IFs) of A1 reactive astrocytes are largely composed of GFAP alone, and the ablation of GFAP is sufficient for suppressing hypertrophic morphology
Summary
The first observation of neuroglia, made by Rudolf Virchow in 1858, was rather dubious. Systematic analysis of the molecular organization of IFs revealed a typical tripartite structure, a globular N terminus (head) and C terminus, connected by a central α-helical domain (the “rod”) with a number of coiled-coil segments of conserved size [28] Based on their amino acid sequence, protein structure and tissue-specific expression patterns, IFs were initially classified into five groups [29]; after the discovery of nestin, Group VI was added to the classification [30]. In the years that followed, astrocytes were shown to express vimentin, nestin, synemin and lamins, which intricately interact with each other as well as with other filament types
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